1. Field of the Invention
The present invention relates to an apparatus and a method for enlarging dot matrix data.
2. Description of the Related Art
There is a case in which dot matrix data output for a printer of a low printing density is supplied to a printer of a high printing density. In this case, keeping an image to be printed to the desired size requires the printer to enlarge the received dot matrix data, i.e., to enlarge the size of dot matrix pattern data; the expression hereinafter is used in this sense. Assume now that dot matrix data output for an impact printer having a printing density of 180 DPI (dots per inch) is supplied to a liquid crystal printer with a printing density of 240 DPI. To maintain the size of the image to be printed to the original value, the liquid crystal printer should magnify the dot matrix data by 4/3 in both row and column directions.
There are two known methods for enlarging dot matrix data:
(1) To enlarge a specific bit of dot matrix data by a predetermined number. A specific example of this method is illustrated in FIG. 1A. In the illustrated example, the third bit of 3-bit dot matrix data is arranged at the third and fourth bits of enlarged 4-bit data.
(2) To enlarge the data size by acquiring a logical sum of adjoining bits of dot matrix data and using it as bit data of new dot matrix data. A specific example of this method is shown in FIG. 2A. In the illustrated example, a logical sum of bit data of the first and second bits of 3-bit dot matrix data serves as bit data of the second bit of new dot matrix data, and a logical sum of bit data of the second and third bits of the original dot matrix data likewise serves as bit data of the third bit of the new dot matrix data.
The above two methods cannot enlarge dot matrix data with high fidelity.
For instance, if 3.times.3 dot matrix data shown on the left side in FIG. 1B is magnified by 4/3 using the first method shown in FIG. 1A, dot matrix data after enlargement would be as illustrated on the right side in FIG. 1B. If 3-bit data shown in the upper half in FIG. 2B is magnified by 4/3 using the second method shown in FIG. 2A, enlarged dot matrix data would be as illustrated in the bottom half in FIG. 2B.
As should be obvious from the above, the prior art methods, when used to enlarge dot matrix data, degrade the quality of a printed image.